Development and application of non-conventional luminophores with aggregation based emission

Nonconventional luminophores without long conjugated structures have received increasing attention due to their outstanding biocompatibility, easy preparation, environmental friendliness, and potential applications in sensing and imaging. The phenomena of aggregation emission, such as concentration-enhanced emission, aggregation-induced emission, excitation-dependent luminescence, and prevailing phosphorescence, are caused by molecular conformation and molecular packing. Herein, we briefly review the traditional luminophores represented by fused aromatic rings, and introduce the revolutionary concept of aggregation induced emission (AIE) in non-traditional luminescence and its applications in optics, biology, and other fields. The concept of the AIE can be applied to understand this phenomena in the field of non-traditional luminescence, in which non-aromatic systems contain electron-releasing and withdrawing parts, such as amine, amide, nitrile, imine, hydroxyl, carbonyl, etc. Moreover, we also address two mechanisms of cluster triggered emission (CTE) and crosslink-enhanced emission (CEE). Based on the reviewed data, we can conclude that the electron overlap caused by aggregation and through-space conjugation (TSC) have a profound impact on unconventional luminescence. We believe that this review would serve as a useful guide to design and application of unconventional luminophores, while the current challenges and future perspectives are also discussed.